Orthogonal Frequency Division Multiple Access (OFDMA) technology is popular in modern communication systems since this technology can efficiently support multiple mobile stations with limited bandwidth and easily provide Quality of Service (QoS). The OFDMA technology is a multiple access version of orthogonal frequency-division multiplexing (OFDM). OFDM is a modulation technique for data transmission based on frequency-division multiplexing (FDM), which uses different frequency channels to transmit multiple streams of data. In OFDM systems, a wideband channel is divided into multiple narrow-band orthogonal “subcarriers” in the frequency domain, each of which is modulated by digital signal in parallel.
In OFDMA systems, multiple subscribers can simultaneously use different subcarriers for signal transmission. Thus, in an OFDMA system, multiple data bursts can be transmitted from a base station (BS) to multiple mobile stations in the same time frame but allocated in different frequency subcarriers. Consequently, an OFDMA system can support multiple mobile stations using different subcarriers.
At a transmitter of an OFDMA system, input information is assembled into blocks of N complex symbols, one for each subcarrier. An N-point inverse Fast Fourier Transform (FFT) is then performed on each block, and the resultant time domain signal is transmitted. Usually, several blocks are grouped to form a frame, and one extra block with known pattern, which is referred to as the “preamble”, is inserted into the beginning of every frame for signal detection, synchronization and channel estimation purposes.
At a receiver of the OFDMA system, the presence of signal needs to be detected and the starting point of a frame needs to be estimated. In addition, a BS needs to be detected and set as the serving BS. Furthermore, in order to synchronize to the transmitter, frequency offset from the serving BS needs to be estimated, which can be challenging in the presence of interference signals. The frequency offset estimate can then be used to synchronize to the serving BS.
In view of these requirements, there is a need for an OFDM-based device and method for performing synchronization even in the presence of interference signals.